docs: def collapse_all_variants(graph) -> None:
      """Collapse all genes', RNAs', miRNAs', and proteins' variants to their parents.
  
      :param pybel.BELGraph graph: A BEL Graph
      """
      has_variant_predicate = build_relation_predicate(HAS_VARIANT)
  
      edges = list(filter_edges(graph, has_variant_predicate))
  
      for u, v, _ in edges:
          collapse_pair(graph, survivor=u, victim=v)
  
      _remove_self_edges(graph)